Unusual chemical transformations of acetone thiosemicarbazone mediated by ruthenium: C-H bond activation, thiolation, and C-N bond cleavage

Article abstract of DOI:10.1039/c3ra44329a

Upon reaction with Ru(PPh₃)₃Cl₂ in ethanol in the presence of triethylamine, acetone thiosemicarbazone undergoes several interesting chemical transformations, such as thiolation via methyl C-H bond activation, C-N bond cleavage, and conversion of the CS fragment to CO. Two complexes (1 and 2) were obtained from this reaction, both of which contained a modified thiosemicarbazone coordinated in SNS- or SNO-mode, two triphenylphosphines and a N-bound thiocyanate. The crystal structures of both the complexes have been determined. Theoretical and mass spectral studies have been carried out to probe the transformations. These complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on both the complexes show a reversible oxidation near 0.6 V vs. SCE, followed by an irreversible oxidation near 1.2 V vs. SCE. DFT calculations have been carried out to explain the electronic spectra, as well as the electrochemical observations.

Full text of DOI:10.1039/c3ra44329a

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Unusual chemical transformations of acetone
thiosemicarbazone mediated by ruthenium: C–H
bond activation, thiolation, and C–N bond
cleavage†
Cite this: RSC Adv., 2014, 4, 1432
a
a
b
Piyali Paul, Dipravath Kumar Seth, Michael G. Richmond
and Samaresh Bhattacharya*a
3 3 2
Upon reaction with Ru(PPh ) Cl in ethanol in the presence of triethylamine, acetone thiosemicarbazone
undergoes several interesting chemical transformations, such as thiolation via methyl C–H bond
activation, C–N bond cleavage, and conversion of the C]S fragment to C]O. Two complexes (1 and 2)
were obtained from this reaction, both of which contained a modified thiosemicarbazone coordinated in
SNS- or SNO-mode, two triphenylphosphines and a N-bound thiocyanate. The crystal structures of both
the complexes have been determined. Theoretical and mass spectral studies have been carried out to
probe the transformations. These complexes show intense absorptions in the visible and ultraviolet
regions. Cyclic voltammetry on both the complexes show a reversible oxidation near 0.6 V vs. SCE,
followed by an irreversible oxidation near 1.2 V vs. SCE. DFT calculations have been carried out to explain
the electronic spectra, as well as the electrochemical observations.
Received 13th August 2013
Accepted 10th October 2013
DOI: 10.1039/c3ra44329a
www.rsc.org/advances
1
R is reasonable small, such as a methyl group, the formation of
a ve-membered chelate ring (II) is usually observed.
Introduction
2s
The chemistry of thiosemicarbazone complexes of transition
metal ions has been receiving considerable attention, primarily
1
because of the bioinorganic relevance of such complexes.
Systematic studies on the binding of thiosemicarbazones to
selected transition metal ions are of considerable importance in
this respect. However, we have been exploring the chemistry of
transition metal complexes of thiosemicarbazones, mainly
because of the variable binding modes displayed by these
ligands in their complexes, and the present work has originated
out of this exploration. Through a series of studies we have was chosen as the ligand, and ruthenium as the metal center.
observed that the coordination mode of thiosemicarbazones It has been well demonstrated by our earlier studies that this
For the present study acetone thiosemicarbazone (Hactsc)
2
(
depicted by Htsc, where H represents the dissociable acidic particular ligand can readily bind to a metal center, via
proton) is dictated, to a large extent, by the nature of the R
dissociation of the acidic proton, as an NS-donor forming a
fragment. If R is fairly large, like a phenyl group, then a four- ve-membered chelate ring (III). The source of ruthenium
membered chelate ring (I) is usually formed. However, when used was Ru(PPh ) Cl , which is well known to undergo facile
1
2
s
1
2r–u
3
3
2
reactions with organic ligands having an acidic proton
3
(
3 2 2
denoted by HL), affording bis-complexes of type Ru(PPh ) L .
The primary aim of the undertaken study was to synthesize a
bis-thiosemicarbazone complex of ruthenium with triphenyl-
phosphine as the ancillary ligand, and examine the binding
mode of the thiosemicarbazone in the complex. During its
interaction with Ru(PPh ) Cl , acetone thiosemicarbazone was
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata
–
b
700 032, India. E-mail: samaresh_b@yahoo.com; Fax: +91-33-24146223
Department of Chemistry, University of North Texas, Denton, TX 76203, USA
†
Electronic supplementary information (ESI) available: Possible resonance
3
3
2
structures in the SNS- and SNO-chelated ligands in IV and V (Fig. S1 and S2),
contour plots of the HOMO and LUMO of complex 2 (Fig. S3) and cyclic found to undergo several unusual chemical transformations,
voltammograms of complex 1 (Fig. S4). Atomic coordinates for the species and the transformed species coordinated to the ruthenium
depicted in Scheme 1 are available from M.G.R. upon request. CCDC 932348
center to afford two interesting complexes, 1 and 2. Herein we
and 932349. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c3ra44329a
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wish to report our ndings on the formation and properties of unprecedented. It is also worth noting that the generation of
these two complexes.
a thiocyanate ion, via degradation of a thiosemicarbazone
ligand is, to our knowledge, also unprecedented. Thus, the
formation of complex 1, as well as of complex 2 (vide infra),
was associated with two novel transformations of acetone
thiosemicarbazone.
Results and discussion
Syntheses and structures
The structure of complex 2 (Fig. 2) was found to be very
similar to that of complex 1, where the ruthenium
center was again coordinated to two triphenylphosphines,
The reaction of acetone thiosemicarbazone (Hactsc) with
Ru(PPh ) Cl in a 2 : 1 molar ratio was carried out in reuxing
3 3 2
ethanol in the presence of triethylamine. This afforded two
complexes, a green complex (1) and an orange complex (2), in
decent yields. Preliminary characterization data (C, H, N
analyses, IR spectroscopy and NMR spectroscopy) for
these complexes clearly indicated that neither of them
were a simple bis-complex of the expected type, viz.
a
thiocyanate (N-bound), and
a
modied acetone
thiosemicarbazone. However, in the modied acetone thi-
osemicarbazone, in addition to thiolation of a terminal
methyl-carbon as observed in complex 1, the sulfur in the
–
C(]S)NH fragment had been replaced by an oxygen atom,
2
and the transformed ligand was coordinated to the metal
center as a tridentate SNO-donor (V). The anionic SNO-
coordinated ligand is also resonance stabilized (Fig. S2,
ESI†), like the SNS-ligand in complex 1, and the observed
metrical parameters (Table 1) within the chelate V are in
accordance with the resonance hybrid structure of this
anion (Fig. S2, ESI†).
The formation of complexes 1 and 2, involving several
unusual chemical transformations of acetone thio-
semicarbazone, is truly intriguing. Though it is not possible to
provide an exact mechanism behind the formation of these two
complexes, a few speculated steps, which seem probable, are
shown in Schemes 1 and 2. The formation of complex 1 is
3 2 2
Ru(PPh ) (actsc) . These characterization data also hinted
that acetone thiosemicarbazone had probably undergone
some unexpected chemical transformations during the
course of the synthetic reaction. For an unambiguous char-
acterization of these two complexes, with a particular refer-
ence to nding out the nature of the transformed acetone
thiosemicarbazone in them, their structures were deter-
mined by X-ray crystallography. The structure of complex 1 is
shown in Fig. 1 and selected bond parameters are given in
Table 1. The structure revealed that acetone thio-
semicarbazone had indeed gone through signicant chem-
ical transformations during the formation of this complex.
For example, it had undergone thiolation at a terminal
methyl-carbon via methyl C–H bond activation, and the
modied thiosemicarbazone was coordinated to ruthenium
as a monoanionic tridentate SNS-donor, forming two adja-
cent ve-membered chelate rings (IV). Two triphenylphos-
phines were also coordinated to ruthenium, and they were
mutually trans. The remaining sixth coordination site on the
metal center was occupied by a thiocyanate ion, which was
linked to ruthenium through the nitrogen. This thiocyanate
ion seems to have originated from the chemical degradation
of another molecule of acetone thiosemicarbazone via a C–N
bond cleavage. It should be mentioned here that although a
localized charge description of the mono-anionic SNS-coor-
dinated ligand is presented in IV, actually the anionic ligand
is resonance stabilized (Fig. S1, ESI†) and the observed bond
parameters within the S–C–C–N–N–C–S fragment (Table 1)
are consistent with the resonance-hybrid structure of this
anionic ligand (Fig. S1, ESI†). It is relevant to mention here
that although metal-mediated thiolation of aromatic carbon
4
has been reported in the literature, such thiolation of an
Fig. 1 (a) Molecular structure of complex 1 (hydrogen atoms are
alkyl carbon, as observed in our present study, appears to be omitted for clarity) and (b) view of the equatorial plane.
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Table 1 Selected bond distances and bond angles for complexes 1 be thermoneutral. In A, the metal center is formally ve-
and 2
coordinated, and hence it is a 16-electron species. Thus an
agostic interaction between the metal center and a proximal
1
methyl C–H, which is common in coordinatively unsaturated
5
˚
complexes of ruthenium(II), seems inevitable. This makes the
Bond distances (A)
Ru(1)–S(1)
Ru(1)–S(2)
Ru(1)–N(1)
Ru(1)–N(11)
Ru(1)–P(1)
Ru(1)–P(2)
S(1)–C(1)
2.3321(17)
2.3789(18)
1.986(5)
C(2)–N(1)
N(1)–N(2)
N(2)–C(3)
C(3)–S(2)
C(2)–C(4)
N(11)–C(11)
C(11)–S(11)
1.340(8) methyl-carbon electrophilic, and, as
a consequence, it
1.355(7)
undergoes an interaction with the nucleophilic sulfur-center of
another molecule of the thiosemicarbazone, leading to the
formation of a new C–S bond, and thus a second intermediate,
1.327(9)
1.716(7)
1.496(9)
2.065(5)
2.3772(17)
2.3792(17)
1.640(7)
1.166(8) B, is generated. The electron-deciency of the sulfur-center in
1.613(6) B, developed due to its coordination to ruthenium(II), triggers
C(1)–C(2)
1.385(8)
some usual rearrangements, resulting in the cleavage of the
C–S bond in the second thiosemicarbazone, and affords a third
intermediate C, along with elimination of hydrogen and an
178.90(17) organic by-product (bp-1). The thiocyanate ion in complex 1,
ꢁ
Bond angles ( )
S(1)–Ru(1)–N(1)
S(2)–Ru(1)–N(1)
81.91(13)
82.18(13)
S(1)–Ru(1)–S(2)
N(1)–Ru(1)–N(11)
P(1)–Ru(1)–P(2)
164.08(6)
172.50(5)
obviously provided by a third thiosemicarbazone, seems to
result from an initial hydrogen-bonding interaction with the
ruthenium-bound chloride in C, followed by elimination of HCl
(from the adduct D) to generate E, and nally via elimination of
2
˚
Bond distances (A)
Ru(1)–S(1)
Ru(1)–O(1)
Ru(1)–N(1)
Ru(1)–N(11)
Ru(1)–P(1)
Ru(1)–P(2)
S(1)–C(1)
2.299(2)
2.170(4)
1.966(6)
2.050(6)
2.383(2)
2.376(2)
1.681(8)
1.349(11)
C(2)–N(1)
N(1)–N(2)
N(2)–C(3)
C(3)–O(1)
C(2)–C(4)
N(11)–C(11)
C(11)–S(11)
1.342(10) another organic species (bp-2). The stoichiometrically balanced
1.344(9)
reaction for the sequence of events depicted in Scheme 1 is
shown in eqn (1). DFT analysis (see the Experimental section
for details) using a two-level ONIOM approach allowed us to
1.515(12)
1.375(11)
1.304(10)
1.151(11) determine the net free energy for the overall process, and we
1.647(9)
computed the conversion of Ru(PPh
)
Cl
to the thiocyanate
3
3
2
C(1)–C(2)
ꢀ1
complex 1 to be endergonic by 42.5 kcal mol . The driving
force for the formation of complex 1 traces its origin to the
entropic contributions associated with this reaction. The
computed entropy change for this process was ca. 140 eu, a
number whose magnitude reects the release of multiple
ꢁ
Bond angles ( )
S(1)–Ru(1)–N(1)
O(1)–Ru(1)–N(1)
82.89(17)
77.50(2)
S(1)–Ru(1)–O(1)
N(1)–Ru(1)–N(11)
P(1)–Ru(1)–P(2)
160.41(15)
176.30(2)
171.20(8)
molecules of H
by-products.
2
and HCl and the accompanying organic
(
1)
Attempts have also been made to identify the possible
intermediates present during the formation of complex 1 by
6
mass spectrometry. The mass spectrum, recorded aer the
reaction had proceeded for 30 min, showed a weaker peak at m/z
+
¼
755 corresponding to intermediate A (for [A ꢀ Cl] ) and two
much stronger peaks at m/z ¼ 884 and 785 that are assignable to
+
+
7
Fig. 2 (a) Molecular structure of complex 2 (hydrogen atoms are B (for [B ꢀ Cl] ) and C (for [C ꢀ Cl] ), respectively. All these
omitted for clarity) and (b) view of the equatorial plane.
three peaks were detectable up to 1.5 h, aer which the peak
corresponding to A started loosing intensity more rapidly
compared to the other two peaks, and a peak corresponding to
+
+
8
believed to be initiated by the coordination of the thio- complex 1 at m/z ¼ 866 (for [1 + Na ] ) started growing. No
semicarbazone to ruthenium in the expected NS-fashion (I), peaks corresponding to the hydrogen-bonded adduct D and the
with simultaneous elimination of PPh
and HCl to produce an next intermediate E were identied, indicating their transient
3
intermediate, A; ONIOM calculations conrm this rst step to existence. Identication of the rst organic by-product, viz.
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Scheme 1 Probable steps behind the formation of complex 1.
0
bp-1, was also not possible, probably due to its rapid hydrolysis generating the rst intermediate (A ), and the following
to form acetone semicarbazone (see Scheme 2). However, the sequences are believed to be similar to those in Scheme 1 to
second organic by-product, viz. bp-2, was identied in the nally yield complex 2. It is interesting to note that the observed
reaction mixture by GC-MS. The mass spectral studies thus changes to acetone thiosemicarbazone during the formation of
support most of the proposed steps behind the formation of complexes 1 and 2, involved ruthenium-mediated C–S bond
complex 1.
cleavage, as well as a new C–S bond formation, and such reac-
9
The formation of complex 2 (Scheme 2) is imagined to start tions are of crucial signicance in synthetic organic chemistry,
with conversion of the rst organic by-product (bp-1), generated biology, and industry.
during the synthesis of complex 1 (Scheme 1), to acetone sem- The fact that there are three sulfur atoms in complex 1 and
10
11
icarbazone (Hacsc) via its interaction with water present in the the only possible sulfur-provider within the reaction vessel was
reaction medium. This newly formed semicarbazone then acetone thiosemicarbazone, clearly shows the involvement of
undergoes a reaction with Ru(PPh
3
)
3
Cl
2
similar to before, three molecules of acetone thiosemicarbazone in the formation
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Scheme 2 Probable steps behind the formation of complex 2.
of one molecule of complex 1. Though speculative, the same is Table 3 Composition of selected molecular orbitals in the complexes
and 2
1
indicated in Scheme 1. Similarly, for one molecule of complex
, two molecules of acetone thiosemicarbazone are necessary,
2
%
Contribution of
as illustrated in Scheme 2. Thus, assuming equal probability
for the formation of complexes 1 and 2, ve molecules of
acetone thiosemicarbazone are required per two molecules of
fragments to
Contributing
fragments
Complex
HOMO
LUMO
3 3 2
Ru(PPh ) Cl . However the synthetic reaction, originally
1
Ru
8.8
41.9
49.3
0
9.3
42.8
47.9
0
7.9
82.9
6.9
2.3
8.5
81.7
7.7
2.1
intended to prepare a bis-thiosemicarbazone complex, was
carried out with only two moles of thiosemicarbazone per
mole of the ruthenium starting material, which probably
accounts for the relatively low yields of the complexes. This is
further supported by the observation that the same reaction,
when carried out with a 3 : 1 thiosemicarbazone–ruthenium
ratio, yields the two complexes in much better yields (complex
SNS-ligand
thiocyanate
PPh
Ru
SNO-ligand
thiocyanate
PPh
3
2
3
1
: 39%; complex 2: 32%).
and another sharp signal at 3.64 ppm for the NH
2
group.
Spectral properties
Only the signal for the proton in the H–C(]S)– fragment
Magnetic susceptibility measurements showed that both could not be detected, probably due to its overlap with the
the complexes 1 and 2 were diamagnetic, which corresponds broad signals from PPh . Infrared spectra of the complexes
to the bivalent state of ruthenium (low-spin d , S ¼ 0) in 1 and 2 showed many bands of different intensities in the
3
6
1
ꢀ1
them. H NMR spectra of the complexes showed broad 400–4000 cm region. No attempt was made to assign each
signals between 7.35–7.73 ppm for the coordinated PPh
individual band to a specic vibration. However, three
ligands, a sharp signal near 2.0 ppm for the methyl group in strong bands were observed around 516, 692 and 744 cm
3
ꢀ1
the coordinated acetone thiosemicarbazone derived ligand, in both the complexes, indicating the presence of
Table 2 Electronic spectral and cyclic voltammetric data
a
3
ꢀ1
ꢀ1
b
Complex
Electronic spectral data, lmax, nm (3, dm mol cm
)
Cyclic voltammetric data, E, V vs. SCE
c
d
e
e
1
2
582 (3500), 438 (16 400), 272 (66 100)
538 (3300), 420 (11 500), 272 (43 100)
0.63 (67), 1.16
c
d
0.68 (70), 1.22
a
b
ꢀ1
c
In dichloromethane. Solvent: acetonitrile, supporting electrolyte: TBHP, scan rate: 50 mV s
.
E
1/2 value (E1/2 ¼ 0.5(Epa + Epc), where Epa and Epc
d
e
are anodic and cathodic peak potentials, respectively). DE
p
value (where DE
p
¼ Epa ꢀ Epc).
E
pa value.
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was found to be delocalized primarily (ꢂ82%) on the SNS-/SNO-
donor ligand, with little contributions coming from the other
fragments. The lowest energy absorption in both the complexes
is hence assignable to a transition from a lled orbital having
mixed (thiocyanate + SNS-/SNO-donor ligand) character, to a
vacant orbital in the tridentate ligand.
Electrochemical properties
The electrochemical properties of the ruthenium complexes
were studied by cyclic voltammetry in acetonitrile solutions
(0.1 M TBHP). Each complex showed two oxidative responses on
the positive side of SCE. Voltammetric data are given in Table 2
and a selected voltammogram is shown in Fig. S4 (ESI†). The

rst oxidation occurred near 0.6 V vs. SCE and it was reversible
in nature, while the second oxidation, observed near 1.2 V vs.
SCE, was found to be irreversible in nature. In view of the
composition of the HOMO in all these complexes, the rst
oxidative response is assigned to the oxidation of the coordi-
nated imine-ligand.
Conclusions
The present study thus shows that acetone thiosemicarbazone
readily reacts with Ru(PPh ) Cl , and by coordinating to the
3 3 2
metal center it undergoes three major chemical changes, viz.
thiolation via methyl C–H bond activation, C–N bond cleavage
to generate the thiocyanate ion, and conversion of the C]S
fragment to C]O to produce acetone semicarbazone. All these
observed transformations, which are unusual as well as
unprecedented, are believed to be initiated through an agostic
interaction between the 16-electron metal center and a proximal
methyl C–H. Our current research efforts remain centered
on related bond-activation processes and these data will be
published in due course.
Fig. 3 Contour plots of the HOMO and LUMO in complex 1.
ꢀ1
3
coordinated PPh ligands. A broad band near 2092 cm was
observed in both the complexes due to the presence of
coordinated thiocyanate.
Experimental
General procedures
Complexes 1 and 2 were soluble in common organic solvents
like methanol, ethanol, acetone, acetonitrile, dichloromethane, Ruthenium trichloride, was purchased from Arora Matthey,
chloroform, etc., producing green and orange solutions, Kolkata, India. Ru(PPh Cl was prepared by following a
Tetrabutylammonium hexa-
3
)
3
2
12
respectively. Electronic spectra of the complexes were recorded reported
procedure.
in dichloromethane solutions. Each complex showed intense urophosphate (TBHP), obtained from Aldrich, and AR grade
absorptions in the visible and ultraviolet regions (Table 2). The acetonitrile, procured from Merck, India, were used for the
absorptions in the ultraviolet region are believed to be due to electrochemical work. All other chemicals and solvents were
transitions within the orbitals of the SNS-/SNO-coordinated reagent grade commercial materials and were used as received.
ligand. To have an understanding of the origin of the lowest- Microanalyses (C, H, N) were performed using a Heraeus Carlo
energy absorption, DFT calculations were performed on both Erba 1108 elemental analyzer. Mass spectra were recorded with
the complexes. Compositions of the highest occupied molec- a Micromass LCT electrospray (Qtof Micro YA263) mass spec-
ular orbitals (HOMOs) and the lowest unoccupied molecular trometer. IR spectra were obtained on a Shimadzu FTIR-8300
orbitals (LUMOs) are given in Table 3. Contour plots of these spectrometer with samples prepared as KBr pellets. Electronic
orbitals for complex 1 are shown in Fig. 3, and those for spectra were recorded on a JASCO V-570 spectrophotometer.
complex 2 are shown in Fig. S3 (ESI†). In both the complexes, Magnetic susceptibilities were measured using a Sherwood
the HOMO had a maximum (ꢂ48%) contribution from the MK-1 balance. NMR spectra were recorded in CDCl solutions
3
coordinated thiocyanate, a slightly lower (ꢂ42%) contribution on a Bruker Avance DPX 300 NMR spectrometer. Electro-
from the coordinated SNS-/SNO-donor ligand, and a much chemical measurements were made using a CH Instruments
lower (ꢂ9%) contribution from the metal center. The LUMO model 600A electrochemical analyzer. A platinum disc working
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Table 4 Crystallographic data for complexes 1 and 2
1
2
Empirical formula
Formula weight
Crystal system
Space group
C
41
H
36
N
4
S
3
P
2
Ru$0.5CH
3
CN
C
41 36 4 1 2 2 3
H N O S P Ru$0.5CH CN
851.57
triclinic
P1ꢀ
835.57
triclinic
P1ꢀ
˚
a/A
12.509(5)
12.844(5)
13.675(5)
95.721(5)
96.275(5)
104.012(5)
2100.3(14)
2
12.436(5)
12.863(5)
13.394(5)
94.291(5)
94.205(5)
104.931(5)
2054.9(14)
2
˚
b/A
˚
c/A
ꢁ
ꢁ
a/
b/
ꢁ
g/
3
˚
V/A
Z
D
ꢀ3
calcd/mg m
1.358
1.369
F(000)
875
867
Crystal size/mm
0.17 ꢃ 0.12 ꢃ 0.10
0.19 ꢃ 0.15 ꢃ 0.11
T/K
298
298
ꢀ1
m/mm
Collected reections
0.633
34 097
0.057
0.599
26 178
0.066
R
int
Independent reections
9547
5733
a
R1
wR2
0.0630
0.1944
1.20
0.0611
0.1947
1.05
b
c
GOF
P
P
P
P
P
a
b
2
0
2 2
2 2 1/2
c
2
2 2
c
1/2
R
1
¼
||F
0
| ꢀ |F
c
||/ |F
0
|. wR
2
¼ [ [w(F
ꢀ F
c
) ]/ [w(F
0
) ]]
.
GOF ¼ [ [w(F
0
ꢀ F ) ]/(M ꢀ N)] , where M is the number of reections
and N is the number of parameters rened.
electrode, a platinum wire auxiliary electrode and an aqueous
Synthesis of acetone thiosemicarbazone (Hactsc). Acetone
saturated calomel reference electrode (SCE) were used in the thiosemicarbazone was prepared by reacting equimolar
cyclic voltammetry experiments. All electrochemical experi- amounts of thiosemicarbazide and acetone in a 1 : 1 ethanol–
2
s,15
ments were performed under a dinitrogen atmosphere. All water mixture.
Yield: 82%. Anal. calcd for C H N S: C 36.64;
4 9 3
1
electrochemical data were collected at 298 K and are uncor- H 6.87; N 32.06. Found: C 36.61; H 6.90; N 32.03%. H NMR
rected for junction potentials. GC-MS analyses were performed (CDCl , 25 C): d 1.90 (s, CH ), 2.01 (s, CH ), 6.46 and 7.22 (2s,
using a Perkin Elmer CLARUS 680 instrument. The nature of NH ), 8.59 (s, NH). IR (wave number, cm ): 3382, 2161, 1603,
ꢁ
3
3
3
ꢀ
1
2
the HOMO and LUMO levels in complex 1 were investigated by 1511, 1470, 1430, 1367, 1304, 1254, 1163, 1109, 1077, 1025, 866,
DFT molecular orbital calculations using the Gaussian 03 787, 727, 635, 581.
1
3
(
B3LYP/SDD-6-31G) package. The different species in Scheme
Synthesis of complexes 1 and 2. To a solution of acetone
1
were examined computationally using Morokuma's ONIOM thiosemicarbazone (28 mg, 0.21 mmol) in ethanol (40 ml) was
1
4
method using the Gaussian 09 soware suite. All of the added triethylamine (25 mg, 0.25 mmol) followed by
ruthenium-containing species were optimized via a two-level Ru(PPh ) Cl (100 mg, 0.10 mmol). The resulting mixture was
3
3
2
approach with the phenyl groups of the PPh ligands treated as then heated at reux for 6 h to yield a dark brown solution. The
3
the lower of the two levels; all other compounds depicted in solvent was then evaporated to give a solid mass, which was
the scheme were optimized using ab initio DFT methods. For subjected to purication by thin layer chromatography on a
those species analyzed within the two-level treatment, we silica plate. Using 1 : 1 acetonitrile–benzene as the eluant, a
employed an ONIOM method that was dened by a B3LPY/ green band and an orange band separated, which were extrac-
PM6 composition. The phenyl groups (low level) were treated ted with acetonitrile. Evaporation of these acetonitrile extracts
at the semi-empirical PM6 level of theory, while the remaining gave green crystals of 1 and orange crystals of 2.
atoms (high level) were treated within the B3LYP framework.
Complex 1. Yield: 24 mg (27% based on Ru-starting material).
With respect to the high-level treatment of atoms, the ruthe- Anal. calcd for C H N S P Ru: C 58.36; H 4.27; N 6.64. Found:
4
1
36 4 3 2
+
+
nium atoms were described by Stuttgart–Dresden effective C 58.27; H 4.25; N 6.65%. MS (ESI), positive mode: [1 + Na ]
core potentials (ecp) and a SDD basis set, while a 6-31G(d ) 866. H NMR (CDCl , 25 C): d 2.00 (s, 3H), 3.64 (s, 2H), 7.37–
basis set was employed for the remaining atoms. All of 7.73 (2PPh + 1H). C NMR (CDCl , 25 C): d 16.7 (C ), 127.9–
the species in Scheme 1 furnished fully optimized ground- 133.8 (PPh ), 161.7 (SCN), 181.7 (C ), 190.7 (C ), 206.9 (C ).
0
1
ꢁ
3
3
1
ꢁ
3
3
4
3
1
P
3
3
2
1
ꢁ
ꢀ1
state structures based on positive eigenvalues obtained from NMR (CDCl , 25 C): d 28.6. IR (wave number, cm ): 2922,
3
the analytical Hessian. The computed frequencies were 2855, 2092, 1731, 1431, 1263, 1160, 961, 813, 744, 715, 692, 516.
used to make zero-point and thermal corrections to the elec-
tronic energies.
Complex 2. Yield: 18 mg (21% based on Ru-starting material).
Anal. calcd for C H N O S P Ru: C 59.48; H 4.35; N 6.77.
4
1
38 4 1 2 2
1438 | RSC Adv., 2014, 4, 1432–1440
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RSC Advances
Found: C 59.55; H 4.37; N 6.76%. MS (ESI), positive mode: [2 +
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+
+
1
ꢁ
Na ] 850. H NMR (CDCl , 25 C): d 2.01 (s, 3H), 3.64 (s, 2H),
3
3
1
ꢁ
.35–7.51 (2PPh + 1H). C NMR (CDCl , 25 C): d 15.3 (C ),
3 3 4
7
1
(
28.0–134.1 (PPh ), 161.1 (SCN), 177.7 (C ), 191.1 (C ), 207.0
3
3
2
3
1
ꢁ
ꢀ1
1 3
C ). P NMR (CDCl , 25 C): d 30.2. IR (wave number, cm ):
2
6
919, 2850, 2093, 1735, 1436, 1269, 1160, 960, 813, 743, 715,
94, 517.
Crystallography
Single crystals of complexes 1 and 2 were grown by the slow
evaporation of solvent from acetonitrile solutions of the
respective complexes. Selected crystal data and data collection
parameters are given in Table 4. Data on the crystals were
collected on a Bruker SMART CCD diffractometer using
392, 118–130; (d) S. Halder, P. Paul, S. M. Peng, G. H. Lee,
A. Mukherjee, S. Dutta, U. Sanyal and S. Bhattacharya,
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S. Gangopadhyay, P. Karmakar and S. Bhattacharya, RSC
Adv., 2012, 2, 5254–5264; (f) D. K. Seth and S. Bhattacharya,
J. Organomet. Chem., 2011, 696, 3779–3784; (g) S. Datta,
M. G. B. Drew and S. Bhattacharya, Indian J. Chem., Sect. A:
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Acta, 2011, 377, 120–128; (i) P. Paul, S. Datta, S. Halder,
R. Acharyya, F. Basuli, R. J. Butcher, S. M. Peng, G. H. Lee,
A. Castineiras, M. G. B. Drew and S. Bhattacharya, J. Mol.
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D. K. Seth, M. G. B. Drew and S. Bhattacharya, Inorg. Chim.
Acta, 2011, 372, 183–190; (k) S. Basu, R. Acharyya, F. Basuli,
S. M. Peng, G. H. Lee, G. Mostafa and S. Bhattacharya,
Inorg. Chim. Acta, 2010, 363, 2848–2856; (l) S. Dutta,
F. Basuli, A. Castineiras, S. M. Peng, G. H. Lee and
S. Bhattacharya, Eur. J. Inorg. Chem., 2008, 4538–4546; (m)
S. Halder, S. M. Peng, G. H. Lee, T. Chatterjee,
A. Mukherjee, S. Dutta, U. Sanyal and S. Bhattacharya, New
J. Chem., 2008, 32, 105–114; (n) S. Halder, R. J. Butcher and
S. Bhattacharya, Polyhedron, 2007, 26, 2741–2748; (o)
S. Basu, R. Acharyya, W. S. Sheldrick, H. Mayer-Figge and
S. Bhattacharya, Struct. Chem., 2007, 18, 209–215; (p)
R. Acharyya, S. Dutta, F. Basuli, S. M. Peng, G. H. Lee,
L. R. Falvello and S. Bhattacharya, Inorg. Chem., 2006, 45,
1252–1259; (q) S. Dutta, F. Basuli, S. M. Peng, G. H. Lee
and S. Bhattacharya, New J. Chem., 2002, 26, 1607–1612; (r)
I. Pal, F. Basuli, T. C. W. Mak and S. Bhattacharya, Angew.
Chem., Int. Ed., 2001, 40, 2923–2925; (s) F. Basuli,
S. M. Peng and S. Bhattacharya, Inorg. Chem., 2000, 39,
1120–1127; (t) F. Basuli, M. Ruf, C. G. Pierpont and
S. Bhattacharya, Inorg. Chem., 1998, 39, 6113–6116; (u)
F. Basuli, S. M. Peng and S. Bhattacharya, Inorg. Chem.,
1997, 36, 5645–5647.
˚
graphite monochromated Mo Ka radiation (l ¼ 0.71073 A).
X-ray data reductions, structure solutions and renements were
16
done using SHELXS-97 and SHELXL-97 programs. The struc-
tures were solved by direct methods.
Acknowledgements
We sincerely thank the referees for their constructive
comments, which were very useful in preparing the revised
manuscript. Financial assistance received from the Department
of Science and Technology, New Delhi [Grant no. SR/S1/IC-29/
2009] is gratefully acknowledged. Piyali Paul thanks the Council
of Scientic and Industrial research, New Delhi, for her
fellowship [Grant no. 09/096(0588)/2009-EMR-I]. Financial
support from the Robert A. Welch Foundation (Grant B-1093-
MGR) is appreciated, as is the NSF support of the computational
facilities at UNT (CHE-0741936). M.G.R. acknowledges helpful
ONIOM discussions with Dr David A. Hrovat (UNT).
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6
7
For the mass spectral study, aliquots of 0.1 ml were taken
from the reaction bed aer certain time intervals and the
aliquots were frozen immediately in liquid nitrogen. These
samples were brought to room temperature prior to mass
spectral analysis and the spectra were recorded as soon as
possible.
The mass spectrum also shows a much weaker peak at m/z ¼
0
0
+
7
39, corresponding to the intermediate A (for [A ꢀ Cl] )
shown in Scheme 2.
8
9
A peak corresponding to complex 2 at m/z ¼ 850 (for [2 +
+
+
Na ] ) also started showing up.
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1440 | RSC Adv., 2014, 4, 1432–1440
This journal is © The Royal Society of Chemistry 2014